The invention relates to an apparatus for shading surfaces or areas, in particular for shading spaces which can be negotiated on foot, or the like, comprising at least a roof sheathing which is stretched on supports or the like carrier elements at a spacing relative to the surface to be shaded, or a corresponding cable netting assembly, as a carrier assembly, on the outside of which are provided photovoltaic elements.
Such an apparatus with silicon crystals which are fixed on the roof sheathing or the cable netting assembly and which are possibly movable relative to each other is described for example in German laid-open application (DE-OS) No 34 27 574. The term photovoltaic elements means, for example, solar cells with a semiconductor plate which in principle is of a double layer configuration, namely an upper negatively doped layer (for example silicon with phosphorus atoms) and a lower positively doped layer (boron atoms). A voltage occurs at an electrical barrier which is provided between the layers, direct current can be taken off directly by way of metal contacts, and can then be adapted to the current mains by inverters. For that reason such photovoltaic elements are also connected directly to current lines.
In accordance with German laid-open application (DE-OS) No 31 42 129, a photovoltaic solar module is strengthened by a galvanized iron wire mesh or gauze which carries a layer of lacquer and is connected to the plastic material enclosing the solar cell, with the interposition of a multi-layer foil as a vapor diffusion barrier. A glass cloth and the electrical lines can extend in the plastic material. Outside the region of its solar cell, which is backed by stiff material, that solar module is capable of being adapted to curved rigid surfaces such as uneven ground, motor vehicle roofs, rock faces, house fronts or the like, and such adaptation to the curved configuration therefore occurs, in such a way as to define the appropriate shape, on a single occasion, namely when the assembly is fitted in position. For, movable non-rigid curved surfaces, solar modules of that kind are just as unsuitable as photovoltaic layers of amorphous silicon or of cadmium derivatives, in accordance with U.S. Pat. No. 3,411,050.
In accordance with German laid-open application (DE-OS) No 34 27 574, those elements which are combined together in solar modules are applied to vibrating or oscillating roofing systems of large area. The particular circumstances of such structures which are referred to as `lightweight areal load-bearing assemblies` give rise to specific requirements in regard to fixing of the solar modules. The following limit values which are governed by snow and wind loading are specified by the specification IEC 504 from the Commission of the European Community, in respect of upstanding roof surfaces which are suitable for the use of solar modules:
Suction forces 2400N/m 2; PA1 Pressure forces 5400N/m 2; PA1 Shearing forces at 60.degree. C.--angle of pitch 5000N/m 2.
Membranes of mesh-like or netting-like fabrics or cable netting assemblies as represents, for example, the roofing of the Olympic Stadium in Munich are usually fitted in a point-like fashion on steel pylons or towers and stretched by means of what are known as bracing riggings to provide cross-sectionally curved, synclastic or anticlastic surfaces. In spite of the prestressing forces applied to them, they experience further slight stretching movements under the effect of snow and wind loadings and thus perform what might be called a breathing motion. The following conditions can apply regarding the stretch effects that occur:
______________________________________ *Membrane carrier assemblies: in the warp direction 1-3%; in the weft direction 1-5%; angular displacement up to 10 degrees; **Cable netting carrier Stretch effects up to 1%; assemblies angular displacement up to 10%. ______________________________________
That means that rigid solar modules which are fitted on lightweight areal carrier assemblies must be provided with a fixing mode which can permit the described movements.
In consideration of those factors, the inventors set themselves the aim of so improving an apparatus of the kind discussed above that the photovoltaic solar modules are secured in relation to the above-indicated forces, on the one hand, but on the other hand they are also capable of accommodating the displacements caused by the suspension configuration.